Reactions of monoazadienes with metal carbonyl complexes. 1

Reactions of monoazadienes with metal carbonyl complexes. 1. Reaction of N-alkyl-(E)-crotonaldimine with ruthenium dodecacarbonyl. The molecular struc...
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Organometallics 1988, 7, 423-429

423

Reactions of Monoazadienes with Metal Carbonyl Complexes. 1, Reaction of N-Alkyl-(E)-crotonaldimine with Ru3(CO),,. The Molecular Structure (X-ray) of the Linear 66-Electron Tetraruthenium Cluster RU,(CO)~,,(CH,C=CHCH =NC3H,-i),, Which I s Isolobally Related to [ (q5-C5H5)Ru(C0)(p-C0)], Louis H. Polm, Wilhelmus P. Mul, Cornelis J. Elsevier," and Kees Vrieze Anorganisch Chemisch Laboratorium, University of Amsterdam, J. H. van't Hoff Instituut, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands

Martin J. N. Christophersen and Casper H. Stam Laboratorium voor Kristallografie, University of Amsterdam, J. H. van't Hoff Instituut, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands Received June 26, 1987

Thermal reactions of monoazadienes (E)-CH,C(H)=C(H)C(H)=NR (R-MAD)with RU~(CO)~, in heptane solution at reflux yield the linear tetraruthenium compounds bis[ (a-N,a-C,q2-N=C,q2-C=C)-N-alkyl(12,32)-crotonaldimin-4-yl]decacarbonyltetraruthenium, Ru~(CO)~~(CH~C=C(H)C(H)=NR)~ The molecular structure of the tetranuclear complex with R = i-Pr-has been solved by means of X-ray diffraction. Crystals of C24H24N2010R~4 are triclinic of space group P1,Z = 1, and cell constants a = 8.5139 (4) A, b = 12.9636 (6) A, c = 8.0914 (7) A, a = 106.43 (1)O, @ = 114.78 (l)',and y = 67.62 ( 1 ) O . A total of 2045 reflections have been used in the refinement, which resulted in a final R value of 0.021 (R, = 0.030). The molecule exhibits a centrosymmetric straight-chain geometry and has Ru-Ru distances of 2.7084 (4) 8, (outer) and 2.7819 (5) A (inner). The complex may be viewed as consisting of a central RU,(CO)~(~-CO), core to which two mutually trans disposed q5-ruthenaazacyclopentadienylfragments, (C0),RuC(CH3)=C(H)C(H)=NR (isolobalwith C5H5),are coordinated; hence RU~(CO),~(CH,C=C(H)C(H)=NR), is an , isolobally related analogue of (E)-[(q5-C5H5)R~(CO)(p-CO)]2. The planar Ru-C(CH,)=C(H)C(H)=NR heterocycle has been formed by metalation of the R-MAD ligand. The linear arrangement of the four ruthenium atoms in the 66e cluster is consistent with CVMO theory. The geometry of the cluster and its formation are discussed.

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Introduction Transition-metal carbonyl dusters possess interesting properties with respect to coordination and activation of organic molecules, which observation has led to the assumption that they might serve as (models for) catalysts for a range of chemical processes. The coordination chemistry and reactivity of 1,3-dienes on metal carbonyl fragments is well-documented.' More recently, the versatile coordination chemistry and chemical activation of 1,4diaza-1,3-dienes2 has received ample attention from the groups of, for example, tom Dieck,, F r u h a ~ f and ,~~~ V r i e ~ e .The ~ ~ ~last group has inter alia focused research on the ruthenium-carbonyl-diazadiene chemistry, with particular emphasis on C-C, C-N, and C-H bond formation and bond rupture reactions involving the coordinated c~-diimine.~-'O The combination of good a-donorla-ac(1) Bennett, M. A.; Bruce, M. I.; Matheson, T. W. In Comprehensiue Organometallic Chemistry; Wilkinson, G., Stone, F. G. A,, Abel, E. W., Eds.; Pergamon: Oxford, 1982; Vol. 4, p 691. (2) The 1,4-diaza-1,3-dienes, RN=CHCH=NR, will be abbreviated R-DAB.6 The l-aza-1,3-dienes of general formula RN=C(R1)C(R2)= CR3R4will be abbreviated MAD, which stands for the general class of monoazadienes. The monoazadienyl anion derived herefrom will be denoted MAD-yl. See also ref 22. (3) tom Dieck, H.; Stamp, L.; Diercks, R.; Muller, C. Nouu.J. Chim. 1985, 9, 289. (4) Fruhauf, H.-W.; Landers, A.; Goddard, R.; Kruger, C. Angew. Chem. 1978, 90,56. (5) Fruhauf, H.-W.; Seils, F.; Goddard, R. J.; Ramao, M. J. Organometallics 1985, 4, 948. (6) Van Koten, G.; Vrieze, K. Adu. Organomet. Chem. 1982,21, 151. (7) Vrieze, K.; van Koten, G. Inorg. Chim. Acta 1985, 100, 79. (8)Staal, L. H.; van Koten, G.; Vrieze, K.; van Santen, B.; Stam, C. H. Inorg. Chem. 1981,20, 3598. (9) Keijsper, J.; Polm, L. H.; van Koten, G.; Vrieze, K.; Stam, C. H.; Schagen, J.-D. Inorg. Chim. Acta 1985,103, 137.

0276-7333/88/2307-0423$01.50/0

ceptor characteristics, combined with the flexibility of the diazadiene skeleton, gives rise to several modes of activation of the coordinated diazadiene and hence a large range of stoichiometric as well as catalytic rea~tions.~-'O Relatively little is known about the behavior of monoazadienes (MAD),, containing a conjugated C=CC=N skeleton, toward metal carbonyl fragments. Several coordination modes of MAD ligands to metals, A-D in Figure 1,have been characterized. The 2e a-N coordination (A) in the complexes (MAD)Fe(CO);' and (MAD)2CuC1,12the 2e $-C=C coordination (B)in (MAD)Ni(PPh3)22J3as well as the 4e $-N=C, $C=C bonding mode (C) in (MAD)Fe(C0)314J5 and (MAD)MO(CO)~(PBU~)~,'~ and the bridging 4e a-N, +C=C mode (D) in [(MAD)Ni(PPh3)]212J6 have all been established by X-ray structures. Other examples of 2e- and 4e-bonded MAD ligands were elucidated by spectroscopic mean^.^^,'^ Thus far, no other possible coordination modes of monoazadienes, e.g. 7e (E), have been observed. (IO) Polm, L. H.; Elsevier, C. J.; van Koten, G.; Ernsting, J. M.; Stufkens, D. J.; Vrieze, K. Organometallics 1987, 6, 1096. (11) Nesmeyanov, A. N.; Rybin, L. V.; Stelzer, N. A.; Struchkov, Yu. T.; Batsanov, A. S.; Rybinskaya, M. I. J. Organomet. Chem. 1979,182, 399. (12) See ref 3. B r o c k " , M.; tom Dieck, H.; Klaus, J. J. Organomet. Chem. 1986. 301. 209. (13) Muller, C.; Stamp, L.; tom Dieck, H. J. Organomet. Chem. 1986, 308, 105. (14) De Cian, A.; Weiss, R. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1972, B28, 3264. (15) Otsuka, S.; Yoshida, T.; Nakamura, A. Inorg. Chem. 1967, 6,20. (16) Walther, D. 2.Anorg. Allg. Chem. 1977, 431, 17. (17) Kang, J. W.; Maitlis, P. M. Can. J. Chem. 1968, 46, 897. (18) (a) Bellachioma, G.; Cardaci, G. J. Chem. Soc., Dalton Trans. 1977,2181. (b) Kokkes, M. W.; Beentjes, P. C. J.; Stufkens, D. J.; Oskam, A. J. Organomet. Chem. 1986,306,77. 0 1988 American Chemical Society

424

Organometallics, Vol. 7, No. 2, 1988

Polm et al. R

I

co 1

0

R B

A

C

2 a R = I-Pr Zb, R

=

c Hex

Bruker WP 80 apparatus at 20.1 MHz (13C). IR spectra were recorded by using a Perkin-Elmer 283 spectrophotometer. Mass spectra (field desorption, FD) were obtained on a Varian MAT 711 double-focusing mass spectrometer with a combined EI/ Elemental analysis FD/FI ion source as described else~here.2~ were carried out by the section Elemental Analyses of the Institute for Applied Chemistry, TNO, Zeist, The Netherlands. All preparations were carried out in an atmosphere of purified D E nitrogen, using carefully dried solvents. Silica gel for column Figure 1. Some possible coordination geometries of metal-mochromatography (Merck, 60 Mesh) was dried and activated before noazadiene complexes. use. R U ~ ( C Owas ) ~ ~obtained from Strem Chemicals, Ltd. The monoazadienes N-isopropyl-(E)-crotonaldimine (la) and NIntramolecular interactions of sp2C-H fragments have cyclohexyl-(E)-crotonaldimine (lb) were prepared from (E)-crobeen observed in de metal-diazadiene complexes, e.g. Pdtonaldehyde and the relevant primary amine according to standard procedures." The compounds were distilled at 0.2 mmHg and (11)" and Rh(I),12and also in (MAD)2Rh(CO)C1,12 but no were stored at -80 "C. NMR data are collected in Tables IV and metalation occurred in these instances. Interestingly,inV. sertion of Ir(1) in the 7-C-H bond of (E)-PhC(H)=CSynthesis of Ru,(CO)lo(CH3C=C(H)C(H)=NC3H7-i)z (2a). (H)C(H)=NC,H,-i occurs readily in a reaction of this R U ~ ( C O (0.64 ) ~ ~ g, 1.0 mmol) and monoazadiene la (0.17 g, 1.5 ligand with Ir(PPh3)2(CO)C1.20Such behavior has not mmol) were stirred under reflux in 50 mL of heptanes (bp 98.5 been observed in da complexes like (MAD)Fe(CO),, but "C, bath temperature a.125 "C). After 20 h, the orange solution j3-C-H activation occurs in reactions of MAD'S with H2was cooled to 20 "C and the orange/red precipitate was collected. Possibly, the propensity of Ru to form ocThis solid was then chromatographed on a silica gel column, tahedral ds complexes might favor metalation of the N= employing first hexane and then dichloromethane as the eluent. CC=C skeleton. If this would be the case, then a formally The hexane fraction contained as yet unidentified products. The orange-red dichloromethane fraction was concentratd, and hexane monoanionic monoazadienyl (MAD-yl)2 ligand RN=Cwas allowed to evaporate slowly into the solution. This afforded (H)C(H)=C-R or RN=C(H)C-=C(H)R would arise, the orange-red crystals in 32% (0.22 g, 0.24 "01) yield of 2a. Anal. former being isoelectronic with a-diimine ligands RN= C, 31.39 (31.79);H, 2.93 (2.89); C(H)C(H)=NR. Hence, complexes like HRU~(CO)~- Found (Calcd for C,H,NzOl&u& 3.07 (3.09); 0,16.87 (17.65). FD-mass: m / z 906 (904).25 IR (MAD-yl)2that are structurally related to RU~(CO)~(R- N, (v(CO)/cm-'): 2059 (s), 1999 (s), 1994 (br, s), 1946 (m), 1750 (s) DAB)2may be expected to emerge from reactions of ruin KBr disk; 2067 (s), 2005 (m), 1993 (s), 1951 (w), 1775 (m) in thenium carbonyls and I. hexane; 2065 (vs), 2OOO (8, sh), 1992 (vs), 1943 (w), 1762 (m) in CHZCl2. NMR data: see Tables IV and V. H Synthesis of Ru4(CO)lo(CH3C=C(H)C(H )=NCeHll-c) \ /R (2b). The same procedure as for the synthesis of 2a was followed, H\ /C=N using 0.23 g (1.5 mmol) of lb. The yield of 2b amounted to ca. 30% (0.21 g, 0.22 mmol). Anal. Found (Calcd for H J C /c=c H ' C&I~ZN~O&U~): C, 36.51 (36.58);H, 3.31 (3.27);N, 2.78 (2.84); 0,16.10 (16.21). FD-maas: m/z 946 (944). IR (v(CO)/cm-'): 2066 1a R 1-Pr (s), 2003 (m), 1992 (s), 1950 (w), 1772 (m) in hexane. NMR data: 1b , R = c-Hey see Tables IV and V. Crystal Structure Determination of Bis[ (o-N,u-C,$-N= It was anticipated that monaazadienes like N-substilZ,3Z)-crotonaldimin-4-yl]decaC,~2-C=C)-N-isopropyl-( tuted crotonaldimines 1 (R-CAI)22derived from (E)-crocarbonyltetraruthenium, Ru~(CO)~~(H~CC=C(H)C(H)= NC3Hri)2(C%HzrNzO1&u4, 2a). Crystals of the title compound tonaldehyde might be likely candidates to stabilize several are triclinic of space group PI,2 = 1, and cell constants a = 8.5139 di- and polynuclear Ru clusters. Therefore, and in order /3 = (4) A, b = 12.9636 (6) A, c = 8.0914 (7) A, a = 106.43 (l)", to see whether descending the triad from Fe to Ru may 114.78 (l)", y = 67.62 (l)", V = 741.6 (1) A3, ddd = 2.03 g ~ m - ~ , lead to insertion of Ru into one or more C-H bonds of the and ~ ( C Ka) U = 170.9 cm-'. The crystal dimensions are 0.07 X monoazadiene, we started our investigations with thermal 0.08 X 0.15 mm. A total of 2520 intensities (2 < 0 < 65") were reactions between RU,(CO)~~ and R-CAI's la and lb. measured on a Nonius CAD4 diffractometer using graphitemonochromated Cu K a radiation, of which 475 were below the Experimental Section 2.50(0 level and were treated as unobserved. The intensities were corrected for Lorentz and polarization factors. Absorption corMaterials and Apparatus. NMR spectra were obtained on rection was deemed unnecessary in view of the small and relatively a Bruker WM 250 spectrometer a t 250.13 MHz ('H) and on a even dimensions of the crystals. The structure was solved by means of the heavy-atom method. Refinement proceeded by means of block-diagonal least-squares calculations, anisotropic (19) van der Poel, H.; van Koten, G.; Vrieze, K. Inorg. Chem. 1980,19,

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1145. (20) (a) van Baar, J. F.; Vrieze, K.; Stufkens, D. J. J. Organomet. Chem. 1975,85, 249. (b) Ibid. 1976,97, 461. (21) Adams, R.D.;Selegue, J. P. Znorg. Chem. 1980, 19, 1795. (22) MAD is used as acronym for monoazadienes in general. In this paper we will use R-CAI when N-alkyl-(bn-crotonaldinines CH3C(H)= C(H)C(H)=NR are meant. k-cM-yl stands for the corresponding a m dienyl anion [CH,C-C(H)C(H)-NR]-.

(23) Staal, L.H.;van Koten, G.; Fokkens, R. H.; Nibbering, N. M. M. Inorg. Chin. Acta 1981,50, 205. (24) Barany, H.C.; Braude, E. A.; Pianka, M. J. Chem. SOC.1949, 1898.

(25) Based on the highest peak of the isotope attern of the molecular ion, calculated value in parentheses based on 'Ru.

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Organometallics, Vol. 7, No. 2, 1988 425

Reactions of Azadienes with Metal Carbonyl Complexes

0

Table 1. Atomic Coordinates of 2a0 X

Y

z

0.46434 (4) 0.47648 (3) 0.4239 (6) 0.3251 (6) 0.6753 (6) 0.0669 (6) -0.0012 (8) -0.0010 (6) 0.3364 (6) 0.5246 (6) 0.6226 (6) 0.8214 (7) 0.4706 (6) 0.6997 (6) 0.2683 (4) 0.4026 (6) 0.2618 (5) 0.8031 (5) 0.4647 (6) 0.8590 (4) 0.019 (7) 0.053 (9) 0.045 (6) -0.118 (9) 0.022 (8) -0.135 (8) 0.060 (7) 0.242 (6) 0.591 (8) 0.847 (8) 0.888 (7) 0.863 (8)

0.18241 (2) 0.39462 (2) 0.0506 (4) 0.1910 (4) 0.1001 (3) 0.3410 (3) 0.2435 (5) 0.3872 (3) 0.3388 (3) 0.2953 (4) 0.2188 (3) 0.1661 (4) 0.4060 (4) 0.4421 (3) 0.3653 (2) -0.0281 (3) 0.1930 (3) 0.0495 (3) 0.4127 (3) 0.4066 (3) 0.402 (4) 0.211 (5) 0.182 (4) 0.262 (6) 0.331 (5) 0.419 (5) 0.443 (4) 0.396 (4) 0.314 (5) 0.089 (4) 0.161 (5) 0.203 (5)

0.25809 (4) 0.41680 (3) 0.2688 (6) -0.0072 (6) 0.1984 (6) 0.2784 (6) 0.2558 (10) 0.1010 (5) 0.5504 (6) 0.6386 (5) 0.5259 (5) 0.6170 (7) 0.1907 (6) 0.5493 (6) 0.3664 (4) 0.2809 (6) -0.1597 (5) 0.1652 (5) 0.0498 (5) 0.5975 (5) 0.357 (6) 0.383 (9) 0.179 (6) 0.207 (9) 0.013 (8) 0.053 (7) 0.123 (7) 0.594 (6) 0.777 (8) 0.629 (8) 0.550 (7) 0.736 (7)

Figure 2. PLUM and ORTEP drawings of the molecular geometry of RQ(CO)~~(CH~C=C(H)C(H)=NC~H,-~)~ (fa) with the adopted numbering scheme. Table 111. Selected Bond Angles (deg) of 2aa The Metal Carbonyl Part Ru(l)-Ru(2)-Ru(2)* 174.550 (16) R~(2)-C(ll)-O(ll) 177.92 (24) Ru(2)-C(12)-0(12) Ru(1)-C( 1)-0(1) 173.28 (22) R~(2)*-C(12)-0(12) Ru(l)-C(2)-0(2) 178.7 (3) Ru-C-O(terminal) Ru(l)-C(3)-0(3) The Ligand Part 75.18 (14) NC(7)-C(8)

Esd's in parentheses. ~~

The Metal Carbonyl Part 2.7084 (4) Ru(2)*-C(12) C(l)-O(l) 2.7819 (5) C(2)-0(2) 1.899 (3) C(3)-0(3) 1.981 (3) 1.890 (3) C(l1)-O(l1) C(12)-O(12) 1.855 (3) 1.987 (3)

2.098 (3) 1.138 (4) 1.124 (4) 1.135 (4) 1.147 (4) 1.177 (4)

Ru(l)-N Ru(2)-N Ru(l)-C(9)

The Metal Ligand Part Ru(2)-C(7) 2.123 (2) Ru(2)-C(8) 2.311 (3) Ru(2)-C(9) 2.048 (3)

2.300 (4) 2.311 (3) 2.362 (3)

N-C(7) C(7)-C(8) C(8)-C(9) C(9)-C(lO)

The Ligand 1.358 (3) 1.405 (5) 1.417 (4) 1.495 (5)

1.490 (4) 1.518 (6) 1.510 (4)

Part N-C(4) C(4)-C(5) C(4)-C@)

Esd's in parentheses. for Ru, C, N, and 0 and isotropic for H. The H-atom positions were derived from a AE'synthesis. A weighting scheme w = 1/(2.2 F, 0.00738'2) was used, and the anomalous scattering of Ru was taken into account. The final R value was 0.021 (R,= 0.030). A final difference synthesis revealed no excursions above +0.5 and -0.9 e/A3. The calculations were performed with XRAY-76. The scattering factors and the dispersion corrections were taken from the literature.26

+ +

Results and Discussion Molecular Structure of 2a. The molecular geometry of 2a with the adopted numbering scheme is shown in the (26) (a) Cromer, D. T.; Mann,J. B. Acta CrystalZogr., Sect. A Cryst. Phys., Dzffr., Theor. Gen. Crystallogr. 1968, A H , 321. (b)International Tables for X-Ray Crystallography; Kynoch Press: Birmingham, Eng land, 1974; Vol. IV. (c) Stewart,J. M. The X-Ray System, Technical Report TR 446 Computer Science Center: University of Maryland, College Park, MD, 1976.

116.9 (3) 116.2 (4) 108.8 (4) 113.6 (3) 74.4 (3) 127.64 (21) 13.3 (3) 130.50 (22)

Table 11. Selected Bond Lentzths (A) of 2aa Ru(l)-Ru(P) Ru(2)-Ru(2)* Ru(l)-C(l) Ru(l)-C(2) Ru(l)-C(3) Ru(2)-C(11) Ru(2)-C(12)

179.08 (23) 142.2 (3) 132.00 (25) 177.25 (25)*

Around Ru(1) Ru(~)-Ru(1)-N Ru(P)-Ru( 1)-C(9) Ru(~)-Ru(1)-C( 1) Ru(2)-Ru( 1)-C(2) Ru(P)-Ru( 1)-C(3) N-Ru(l)-C(g) N-Ru(l)-C(l) N-Ru(l)-C(2)

55.56 (7) 57.57 (9) 147.11 (9) 105.70 (11) 109.55 (11) 78.73 (15) 98.87 (18) 98.79 (16)

Ru(l)-Ru(2)-C(12) Ru(1)-R~(2)-C(12)* Ru(l)-Ru(P)-C(ll) N-Ru(2)-C(9) C(ll)-Ru(2)-C(12)

125.88 (9) 139.87 (8) 84.04 (12) 68.97 (14) 91.82 (21)

N-Ru(l)-C(3) C(S)-Ru(l)-C(l) C(9)-Ru(l)-C(2) C(9)-Ru(l)-C(3) C(l)-Ru(l)-C(2) C(l)-Ru(l)-C(3) C(2)-Ru(l)-C(3)

164.65 (13) 100.66 (17) 161.42 (14) 89.94 (19) 97.91 (18) 93.34 (22) 88.64 (19)

Around Ru(2) 48.79 (10) Ru(2)*-Ru(2)-C(l2) 94.22 (18) C(12)*-R~(2)-C(12) 94.65 (14) Ru(2) *-Ru(2)-C( 11) C(12)*-R~(2)-C(ll) 94.44 (17) R u ( ~ ) * - R u ( ~ ) - C ( ~ ~45.44 ) * (8)

Esds in parentheses. Mean value.

PLUTO drawing (Figure 2), also provides an ORTEP view.

Atomic pargmeters and selected bond lengths and angles are given in Tables I, 11, and 111, respectively. The molecule exhibits an essentially centrosymmetric straightchain geometry with the inversion center halfway between Ru(2) and Ru(2)*. There are three single metal-metal bonds. Each of the outermost Ru atoms bears three terminal CO molecules, while the inner two Ru atoms have each one terminal CO (in mutual trans position) and share two asymmetrically bridging CO's. The monoazadienyl ligand is a-N, u-C(9) bonded to Ru(1) and q2-N=C(7), q2-C(8)=C(9) bonded to Ru(2). The overall geometry closely resembles that of H2Ru4(C0)8(R-DAB)2(3).27 However, in 2a no pseudo mirror plane can be defined because of the intrinsic asymmetry of the N=CC=C (27) Keijsper, J.; Polm, L. H.; van Koten, G.; Vrieze, K.; Nielsen, E.; Stam, C. H. Organometallics 1985, 4 , 2006.

426 Organometallics, Vol. 7, No. 2, 1988

Polm et al.

skeleton in 2a compared to N=CC=N in 3. The 66-electron complex 2a may be viewed as a symmetrical dimer, consisting of two linked 33-electron Ru2(CO)5(R-CAI-yl)22 fragments, in which the R-CAI-yl ligands form 7e bridges between the RU(CO)~ and Ru(CO), moieties. Alternatively, the molecule may be imagined as an isolobal analogue of (E)-[ (T~-C,H,)RU(CO)(~-CO)], (4), as will be elaborated below. In this view, 2a consists basically of a central Ru2(CO),(p-CO), core, which is substituted with two mutually trans disposed ruthenaazacyclopentadienyl rings.

effect will occur to a much smaller extent between the relevant Ru atom and the N atoms in, for example, diazabutadiene complexes like 3. Apart from the elongated Ru(l)-C(2) bond, compared to Ru(l)-C(1) and Ru(1)-C(3), the Ru(l)(CO), moiety shows normal bond distances and angles. The longer Ru(1)-C(2) bond is due to the diminished back-donation from Ru(1) to this CO ligand compared to the other CO's, because of *-donation out of the relevant d orbital to C(9) (vide infra). Also, the angle C(2)-Ru(l)-C(3) is smaller than the C(l)-Ru(l)-C(2) and C(l)-Ru(l)-C(3) angles, due to this trans influence of C(9) (and N). The C(2)-RuR R (1)-C(3) angle falls in the range that is generally observed for such an angle trans to a-C and u-N ligand^.'*^^^,^^ An alternative explanation may be the steric interaction that the C(2)-0(2) moiety suffers from the N-isopropyl group, which also accounts for the Ru(l)-C(2)-0(2) angle of R R 173.3', significantly deviating from linearity. The C(12)-0(12) bond in the asymmetrically bridging 3 CO is elongated, as expected, but also the bond order of the C(ll)-O(11) bond is somewhat diminished. The Ru(2)-C(ll) bond distance is shorter than the Ru(1)-CO bonds, indicating higher electron density on Ru(2) compared to Ru(1). The Ru(1)-N distance amounts to 2.123 (2) A, which is in magnitude close to comparable Ru-N distances in H,RU~(CO)~(R-DAB)~ and other low-valent di- and trinuclear ruthenium-diazabutadiene complexes with 8e-do4 nating R-DAB l i g a n d ~ . ~ JThe l > ~Ru-N ~ bond of the pyridine N(sp2)atom to Ru in a dinuclear Ru(1)-Ru(1) comThe most striking feature of the molecular structure is plex amounts to 2.264 (11)A (mean of Pyridine the linear arrangement of the four Ru atoms. The angle in trans position to CO in a low-valent Ru complex has a Ru(l)-Ru(2)-Ru(2)* amounts to 174.55 (Z)', which comreported Ru-N bond length of 2.181 (2) A.35b Clearly, the p a y well with the value of 176.48 (6)' for the related angle Ru-N distance in the present compound 2a is shorter. in H,Ru,(CO)JR-DAB)~~and of 177.0 (1)' and 165.2 (1)' (mean) in [Rh2Mn2(p-dimethyl-2,5-diisocyanohexane)4- Several still shorter Ru-N distances are known, e.g., 2.08-2.12 A36or even as short as 2.02 A in case of a cy(CO)lo]2+28 and Rh2W2(p-PPh2)4(p-C0)2(C0)8,29 respecclometalated a ~ o b e n z e n e Probably, .~~ in such instances, tively. some multiple-bond character due to charge delocalization The intermetallic distances are 2.7084 (4) 8, for Ruin the metallacycle plays a role. Such effects may account (l)-Ru(2) and 2.7819 (5) 8,for Ru(2)-Ru(2)*. These values for the observed Ru(1)-N distance in 2a. The Ru(l)-C(3) are indicative of a bond order of 1 between the metal bond (of CO trans to N) is not appreciably elongated, centers. The Ru(2)-Ru(2)* single bond, which is part of however, so the extent of the effect remains open to the doubly CO-bridged central unit of 2a, is about 0.04 %I question. This contrasts with the effect on Ru(l)-C(2) longer than comparable Ru-Ru bonds in 327and 4.30 The trans to C(9), as discussed above. different Ru(2)-C(12)and Ru(2)*-C(12)distances of 1.987 The Ru(1)-C(9) distance amounts to 2.048 (3) 8, and is (3) and 2.098 (3) A, respectively, reflect the asymmetry of approximately what one would expect for a Ru-C single the bridge caused by the asymmetric coordinated R-CAI-yl bond. Although the precise nature of the single Ru-C(sp2) in 2a. The Ru(l)-Ru(2) distance is significantly shorter bond is subject to controversy (cf. ref 33, 37, 38), a reathan the 2.741 (1)8, in, for example, RU,(CO)~(DAB)~~ or sonable assessment of this length as the sum of the cova2.806 (2) 8,in H2Ru4(CO)8(R-DAB)2n and is a rather short lent radii of Ru in Ru3(CO),2 (1.42 A) and of C(sp2) in Ru-Ru single-bond distance, cf. the Ru-Ru distances of anthracene (0.71 A) would be 2.13 A. This estimation is 2.696 (1)8, in [(T~-C~H~)~RU~(CO)~(~-CO)(~-CCH~)]BF~~~ in concert with observed Ru-C(sp2) distances of 2.128 (4) or 2.717 (1) 8, in RU~(CO)~(~-CO)(C~(CH~CH~OH)~(C2H5)2).33 The short Ru(l)-Ru(2) distance in 2a as compared to 3 may be due to effective charge relay from (34) Keijsper, J.; Polm, L. H.; van Koten, G.; Vrieze, K.; Seignette, P. F. A. B.: Stam, C. H. Inorp. Chem. 1985.24. 518. Ru(2) to Ru(1) to the r-system of the R-CAI-yl ligand (35) (a) Jeannin, S.; J e a k i n , Y.; Lavigne,'G. Transition Met. Chem. back to Ru(2). Such a synergic effect shortens the Ru(Weinheim,Ger.) 1976,1,186. (b) Jeannin, S.; Jeannin, Y.; Lavigne, G. (1)-Ru(2) distance and may be brought about through Transition Met. Chem. (Weinheim, Ger.) 1976, I , 192. (36) (a) Cheng, P. T.; Loescher, B. R.; Nijburg, S. C.; Inorg. Chem. *-overlap of, notably, Ru(1) with C(9) (vide infra). This (28) Mann, K. R.; Dipierro, M. J.; Gill, T. P. J. Am. Chem. SOC.1980, 102, 3965. (29) Shulman, P. M.; Burkhardt, E. D.; Lundquist, E. G.; Pilato, R. S.; Geoffroy, G. L. Organometallics 1987, 6, 101. (30) Mills, 0. S.; Nice, J. P. J . Organomet. Chem. 1967, 9, 339. (31) Keijsper, J.; Polm, L. H.; van Koten, G.; Vrieze, K.; Abbel, G.; Stem, C. H. Znorg. Chem. 1984,23, 2142. (32) Colborn, R. E.; Davies, D. L.; Dyke, A. F.; Endesfelder, A.; Knox, S. A. R.; Orpen, A. G.; Plaas, D. J. Chem. SOC.,Dalton Trans. 1983,2661. (33) Astier, A.; Daran, J.-C.; Jeannin, Y.; Rigault, C. J. Organomet. Chem. 1983,241, 53.

1971, 10, 1275. (b) Restivo, R. J.; Ferguson, G. J . Chem. SOC.,Chem. Commun. 1973, 847. (37) (a) Parkins, A. W.; Fischer, E. 0.; Huttner, G.; Regler, D. Angew. Chem. 1970,82,635. (b) Cox, A.; Woodward, P. J . Chem. SOC.A 1971, 3599. (c) Christian, D. F.; Clark, G. R.; Roper, W. R. J . Organomet. Chem. 1974,81, C7. (d) Clark, G. R. J. Organomet. Chem. 1977,134,51. (38) (a) Blackmore, T.; Bruce, M. I.; Stone, F. G. A. J. Chem. Soc., Chem. Commun. 1971,852. (b) Evans, M.; Hursthouse, M.; Randall, E. W.; Rosenberg, E. J. Chem. Soc., Chem. Commun. 1972,545. (c) Bruce, M. I.; Gardner, R. C. F.; Goodall, B. L.; Stone, F. G. A.; Doedens, R. J.; Moreland, J. A. J. Chem. SOC.,Chem. Commun. 1974,185. (d) Moreland, J. A.; Doedens, R. J. Znorg. Chem. 1976,15, 2486. ( e ) Yamazaki, H.; Aoki, K. J . Organomet. Chem. 1976, 122, C53. (f) Komiya, S.; Ita, T.; Cowie, M.; Yamamoto, A.; Ibers, J. A. J . Am. Chem. SOC.1976, 98, 3874.

Organometallics, Vol. 7, No. 2, 1988 427

Reactions of Azadienes with Metal Carbonyl Complexes

A in a Ru-dimethylimidazolium complex39and of 2.160

(10) A in a (a-naphthy1)ruthenium compound.40 The Ru(l)-C(9) distance of ca 2.05 8, in 2a and reported RuC(sp2)distances in comparable complexes, ranging from 2.02 (1)to 2.09 ( 1)A,33937938 are significantly shorter. It has been suggested37that a Ru-C distance of this magnitude represents some multiple-bond character and may be viewed as a elongated carbene-type bond.37c,dTherefore, and because of the elongated C(8)-C(9) double bond, it seems justified to describe the Ru-C(9) bond as a delocalized secondary carbene linkage.41 The suggestion that electron density from Ru(1) is used for a-bonding with C(9) is corroborated by (i) the observed shortening of the Ru(1)-Ru(2) bond (cf. ref 33) and (ii) the lengthening of the Ru(l)-C(2) bond trans to C(9) (vide supra). The monoazadienyl fragment is coordinated to Ru(2) in a way similar to the a,a-coordination of PhC(H)=C(H)C(H)=NF’h to Fe in the corresponding (MAD)Fe(CO), c0mp1ex.l~ The Ru(2)-N, Ru(2)-C(7), and Ru(2)-C(8) distances are equal within experimental error and amount to 2.311 (4) A (mean). The Ru(2)-C(9) bond length of 2.362 (3) A is significantly (0.05 A) longer. This situation is comparable to that in (MAD)Fe(CO),, where the relevant Fe-C distance is 0.08 A longer than the other Fe-C and Fe-N distances.14 The C(7)-C(8) and C(S)-C(9) bond lengths of 1.405 (5) and 1.417 (4) A, respectively, are comparable to those found in, for example, (a4-C6HB)Fe(co)3,42 and are longer than a C = C double bond (1.33 A) but shorter than a C(sp2)4(sp2)single bond (1.46 A). The N-C(7) bond length of 1.358 (3) A is of the same order of magnitude as the N-C bonds of 1.34 (1)A in pyridine4, and of 1.35 (2) A (mean) in 3. Furthermore, the bond lengths within the R-CAI-yl ligand are (within experimental error) equal to their congeners in (MAD)Fe(C0),.14 The angles N-C(7)4(8) and C(7)-C(8)-C(9)are equal and amount to 116.5 ( 5 ) O . The torsion angle between the N-C(7) and C(8)-C(9) bonds amounts to lo.These facts point to effective delocalization of a-electrons in the NC-C-C subsystem, which was also observed in the N-CC-N moiety in, for example, (R-DAB)M,(CO),L (M = Ru, L = p-CO, p - R ~ ( C 0 ) ~M; ~=~Fe, v ~L = p-HC--=CCOOMeU) and similar complexes like Fe2(C0)6(C6H602)4s and Ru2(CO)6(C4(CH20H)4),33 containing metalla(hetera)cyclopentadiene rings. It has been shown above that the Ru(1)-C(9) and (to a lesser extent) Ru(1)-N bonds are shortened due to aoverlap with the metal; i.e., delocalization of electron , density occurs within the Ru(l)-N-C(7)-C(8)-C(9) ring. The plane containing N, C(7),C(8), and C(9) also contains to a good approximation the Ru(1) atom, which is 0.12 A out of this plane.46 The largest deviation from the plane through Ru(l), N, C(7), C(8), and C(9) amounts to 0.034 A (for N) which is equal to the root-mean-square deviation of 0.029 A for this calculated plane. The sum of the enclosed angles amounts to 539.7’, which value is close to the theoretical 540’ for a pentagon confined to one plane. I

(39) Sundberg, R. J.; Bryan, R. F.; Tay!or, I. F.; Taube, H. J. Am. Chem. SOC.1974,96, 381. (40) Gregory, U. A.; Ibekwe, S. D.; Kilbourn, B. T.; Russell, D. R. J.

Chem. Soc. A 1971, 1118. (41) (a) Cardin, D. J.; Setinkaya, B.; Lappert, M. F. Chem. Rev. 1972, 72,545. (b) Gallop, M. A.; Roper, W. R. Adv. Organomet. Chem. 1986, 25, 121. (c) Roper, W. R. J. Organomet. Chem. 1986, 300, 167. (42) Dickens, B.; Lipscomb, W. N. J. Chem. Phys. 1962, 37, 2084. (43) Sutton, L. E. Tables ofhteratomic Distances and Configurations in Molecules and Ions; The Chemical Society: London, 1965. (44) Muller, F.; Vrieze, K., unpublished results. (45) Hock, A. A.; Mills, 0. S. Acta Crystallogr. 1969, 14,139. (46) For this plane a root-mean-square deviation of 0.006 A was calculated.

Table IV. ‘HN M R Data (ppm) of CHg10C(H9)=C(H8)C(H7)=NR (la,b) a n d of RU~(CO)~~(CH~~~C=C(H~)C(H~)=NR)~ (2a,b)O R-CAI complex

la atom

(R = i-Pr)

7.57 (d, 8.0) 5.91 (m) H(9) 5.91 (m) H(10) 1.59 (d, 5.0) NR 3.03 (sept, 6.3) 0.90 (d, 6.3)

H(7) H(8)

lb (R = c-Hex) 7.67 (d, 8.0) 6.01 (m) 6.01 (m) 1.68 (d, 5.3) 2.77 (m) 1.8-0.8 (m)

2a

2b

(R = i-Pr)

(R = c-Hex)

6.81 (d, 2.0) 5.08 (d. 2.0)

6.83 (br s) 5.07 fbr s)

2.55 (s) 3.53 (sept, 6.5) 1.25 (d, 6.5) 1.17 (d, 6.5)

2.54 ( 8 ) 3.03 (m) 1.8-1.0 (m)

“At 250.1 MHz; solvent CDC13; T = 293 K; multiplicity (s, singlet; d, doublet; sept, septet; br, broad) and J(H,H) (k0.5 Hz) in parentheses.

On the basis of these considerations the ring constituted , , by Ru(l)-N-C(7)-C(8)-C(9) may be imagined as a diheteracyclopentadienyl fragment. In this sense, Ru4(CO)lo(R-CAI-yl)2(2) has become an analogue of [(a5C~H,~RU(CO)(P-CO)I~ (4). FD-Mass Spectrometry. The molecular formulas of 2a and 2b became immediately evident, using this powerful technique for the elucidation of the mass of nonvolatile organometallic compounds. The observed intensity patterns of the molecular ions (see Experimental Section) were successfully compared to computer-simulated patterns. IR v ( C 0 ) Region. The five IR v(C0) frequencies of 2a and 2b (see Experimental Section) are characteristic for these complexes. The centrosymmetric geometry in solution is corroborated by the presence of only five bands for the 10 CO’s. The v(C0) frequencies in the Ru(l)(CO), moiety can be directly compared to those in RU(CO)~(U,~-N,N’-R-DAB)~~~~~ and Fe(C0),(a4-MAD).ls For R U ( C O ) , ( M ~ , C ~ H ~ - D Athe B ) , ~Ru(CO), ~ unit has locally distorted C3” symmetry, as evidenced by a sharp, intense band at 2053 cm-’ (A,) and two bands at 1991 and 1978 cm-’ due to splitting of the E band. The bands of 2a in hexane at 2067,2005, and 1993 cm-’ correlate with these and can be ascribed to the A’ and A’ + A’’ vibrations in the Ru(l)(CO), group, in accordance with the local C, symmetry of the entity. For 2b a similar pattern is observed. These three bands in 2 have shifted toward higher frequencies compared to the Ru(CO),(R-DAB) complex, which indicates less a-back-donation from Ru(1)to these CO’s in 2. This observation is in qualitative agreement with the formal +1 oxidation state of Ru(1) and with the a-bonding of Ru(1) to C(9) as discussed under Molecular Structure of 2a. The v(C0) frequency of the terminal CO on Ru(2) is observed at lower frequency (1951 cm-’) as might be expected for a CO with a lower bond order (see Table 11). The 1775 cm-’ band is found in the stretching region of asymmetrically bridging CO’s and is assigned to the antisymmetric stretching mode of the M2(p-CO),entity. The spectra of 2a and 2b in CH2C12solution are similar to that of 2a in hexane. As the same pattern of v(C0) bands pertains in KBr disk, it can be concluded that the geometry of 2a and 2b in solution is similar to that in the solid phase. NMR Spectroscopy. ‘H NMR. The lH NMR data of the free R-CAI ligands (la,b) and of the tetranuclear complexes 2a,b are listed in Table IV. Due to the C, symmetry of the complexes, only one set of resonances is observed for the two equivalent R-CAI-yl ligands. The resonances of H(7) and H(8) in 2a and 2b have shifted ca. (47) Staal, L. H.; Polm, L. H.; Vrieze, K.; Ploeger, F.; Stam, C. H. Inorg. Chem. 1981,20, 3590. (48) Mul, W. P.; Elsevier, C. J.; Vrieze, K., unpublished results.

428 Organometallics, Vol. 7, No. 2, 1988

Polm et al. Scheme I. Isolobal Relationships'

Table V. 13C NMR Data (ppm) of C'oHJC9(H)=Ce(H)C7(H)=NR (la,b) and of RU~(CO),~(C~~H~C~=C~(H)C~(H)=NR)~ (2a,b)' R-CAI atom c(7) C(8) c(9)

C(l0) NR

la (R = i-Pr) 159.4 138.8 131.7 17.5 60.3 23.5

complex

lb

2a

(R = c-Hex) 159.6 138.8 132.0 17.6 68.8 33.9 25.1 24.3

(R = i-Pr)

'At 20.1 MHz; solvent CDC1,;

T

129.7 102.6 195.9 32.1 61.2 26.0 29.8

2b (R = c-Hex)

4

5 '

129.8 102.4 196.3 32.1 69.2 38.9, 37.6 25.7, 25.4 25.0

t I

= 263 K.

5

1ppm upfield compared to those in the free ligands la and lb. This is consistent with a decreased paramagnetic contribution (induced by the C=X (X = C, N) groups) to the chemical shift, due to q2-coordinatioiiof both N=C(H) and (H)C=C moieties in 2a and 2b. The shift difference between free ligands and complexes is intermediate between that observed in Ru2(CO),(butadiendiyl)of 0.1 ppm d ~ w n f i e l dand ~ ~in Ru,(CO),(R-DAB) of 1.6-2.0 ppm upfield.31 Protons H(7) and H(8) are weakly coupled, 3J = 2 Hz, which is a smaller value than expected. In Mz(CO)&butadienediyl)(M = Fe, Ru, Os) in which the ligand -C (H,)=C(H,)C (H,!)=C(H,)- is u,u-C,C, q2-C=C', $-C=C' bonded to the Mz(CO)6core, a coupling constant of 3J(Hx,Hy) N 3.5 Hz has been observed.49 The singlet of the =C(CH3) protons is found at 2.55 ppm in 2a and 2b. The downfield shift of ca. 1 ppm compared to those of l a and lb implies a more pronounced paramagnetic deshielding, probably due to the proximity of 7r-electron density between Ru(1) and C(9). The diastereotopicity of the N-i-Pr methyl groups is clearly demonstrated by the presence of two separate doublets in the lH NMR of 2a. 1%NMR. The 13CNMR data of the free R-CAI ligands la,b and of the complexes 2a,b are listed in Table V. The signals (except C(9) in 2a,b) have been assigned by l3C(lH] COSY. The upfield shifts of 30 and 36 ppm compared to those of the free ligand for C(7) and C(8), respectively, in 2a as well as in 2b are within the range of upfield shifts that have been observed in complexes M2(CO)6(butadie n e d i ~ l ) Unfortunately, .~~ no 13C NMR data are known for M,(CO),(R-DAB) and HzRu4(C0)8(R-DAB)2. The chemical shift of C(9) in 2a,b (195 ppm) falls within the region of 160-200 ppm where resonances of carbon atoms are found, which are a-coordinated to one Ru atom and 7-coordinatedto another." This chemical shift is also in the neighborhood of values reminiscent of Ru and Os alkyl~arbenes.~'~ Generally, 6 values of such carbene carbon atoms are found slightly more downfield (200-240 ppmh4I In the present case the carbene character of C(9) is less pronounced, in agreement with the X-ray data (vide supra). Anyhow, the large downfield shift relative to the free ligands of 64 ppm for C(9) must be due to an increased contribution to the paramagnetic chemical shift tensor, due to 7-bonding of Ru(1) to C(9). The C(10) atoms of the R-CAI-yl ligands in complexes 2a,b have shifted downfield by 15 ppm compared to the C(l0) signals in free R-CAI, reflecting the proximity of Ru( 1). The diastereotopicity of the carbon atoms of the substituents on nitrogen in 2a and 2b, respectively, is evidenced by the separate signals (49) Aime, S.;Ochiello, E. J. C h e m . SOC.,Dalton Trans. 1986, 1863. (50) Aime, S.;Milone, L.; Osella, D.; Valle, M.; Randall, E. W. Inorg. Chim. Acta 1976,20, 217.

'Half of the molecule of compounds 2 and 4 are drawn.

for all carbon atoms involved. Cluster Geometry. Tetranuclear transition-metal clusters may exhibit several geometric configurations, depending on the number of valence electrons provided by the metal atoms and ligands, that are involved in b ~ n d i n g . ~The ' present Ru4 cluster contains three metal-metal bonds, in agreement with the presence of 66 closed valence electrons (CVE):, indicating that the molecule is electron-precise. In the electron count the a-N, u-C, q2-N=C, q2-C=C coordinated R-CAI-y1 fragment contributes a total of seven valence electrons to the cluster and each Ru atom eight. In the complex, six CVE have been added to the basic tetrahedral M4 configuration with 60 CVE, which contains six metal-metal bonds. The six added electrons occupy three high-lying antibonding cluster valence molecular orbitals, leaving a net bond order of 3 in 2a,b. The linear tetranuclear configuration is favored with respect to the other possible geometry for M4 clusters with 66 CVE, namely, a T or Y configuration, probably because 2a is formed as a linear Ru4species (vide infra), which will not easily isomerize. For M4 clusters containing only transition metals, the T or Y configuration has never been observed. Instead, the straight-chain M4 geometry has been identified in seven cases, including the present one.27-29,53-55 These complexes invariably contain strongly bridging ligands like Ph2P- and CO, indicating that the R-CAI-yl ligand in 2a (like R-DAB in 3) equally forms strong bridges between transition-metal centers and is thus able to stabilize unusual cluster geometries. An attractive alternative Derception of 2a is as a structural analogue of (E)-[(115:C5H5jRu(CO)(~-CO) J 2 (4). In this view the Ru(l)-N-C(7)-C(8)-C(9) heteracycle is imagined as a diheteracyclopentadienyl fragment, which is 05-coordinatedto Ru(2). Credit for this proposal emerges from the formal, isolobal analogy between a (CO),RuN(R)=C(H)C(H)=CCH, fragment and C5H$(Scheme I), since Ru(CO), %L CH+ and RN